The use of communication cables which include a plurality of optical fibers as the transmission media is rapidly expanding. An optical fiber cable may comprise a plurality of glass fibers each of which is protected by at least one layer of a coating material. The optical fibers may be assembled into units in which the fibers are held together by binder ribbons to provide a core. In one manufacturer's line of cables, the core is enclosed by a plastic tube and a plastic jacket.
Whatever the structure of a cable, there must be provisions for connecting, such as by splicing, transmission media at an end of a given length of cable to corresponding transmission media at an adjacent end of another length of cable. It is conventional to use a closure, within which all conductors are connected, wrapped and stored and protected environmentally.
During the connection of metallic conductors, it is customary to bend sharply the conductors, to provide access to other connections. The physical nature of glass optical fibers forecloses the adoption of connectorization techniques which are used with metallic conductors within a closure. Because of their small size and relative fragility, special considerations must be given to the handling of optical fibers in closures. Transmission capabilities may be impaired if an optical fiber is bent beyond an allowable bending radius, the point at which light no longer is totally contained in the core of the fiber. Furthermore, expected lives of the fibers will be reduced if bent to less than the minimum bending radius.
In the prior art, fiber slack normally has been provided adjacent to connective arrangements. When splicing optical fibers by mechanical means or by fusion, it becomes necessary to provide enough slack fiber so that the fiber can be pulled out of a closure and positioned in apparatus for the preparation of fiber ends and the joining together of the ends.
In one prior art closure, a tubular cover having a closed end and an open end is adapted to receive and be sealed to a cable termination assembly. The cable termination assembly includes cable entry facilities through which the cables to be spliced are routed. A support member extends from the cable entry facilities and has a free end disposed adjacent to the closed end of the cover. The support member includes a support base for supporting an optical fiber breakout and a plurality of optical fiber splice trays. Mounted centrally of each tray is at least one organizing module each of which is capable of holding a plurality of optical fiber connective arrangements. Each module is such that it is capable of accommodating different kinds of connective arrangements such as, for example, fusion splices and mechanical splices, both polished and non-polished. Each tray is capable of holding a plurality of organizing modules which may be added as needed.
Closures also are needed for uses other than connecting end portions of newly installed cable lengths. During the service life of an optical fiber cable, the cable may become damaged. This may occur, for example, through unintentional contact by various kinds of excavation equipment, by lightning or by repeated attack by animals such as gophers, for example. Such damage may be partial, in which case one or several optical fibers may be interrupted, or the damage may be total, such as a complete cable cut, for example.
Whatever the structure of the damaged cable, there must be provisions for connecting, such as by splicing, transmission media of the cable on each side of the damage location to corresponding transmission media of a restoration cable which is used to bridge around the damage location. It is conventional to use a closure, within which all fibers are connected, wrapped and stored and protected environmentally.
In any case, it becomes necessary to restore service as quickly as possible. This may be done through an expedited temporary arrangement while more work is under way to replace the damaged cable with an equivalent or enhanced system.
A temporary arrangement which includes a closure must be one which is easily and rapidly installed and which is low in cost. Elements of the arrangement must be capable of being packaged in a kit which is portable and, desirably, in one which may be carried by an individual from a vehicle to a field location at which a disruption to service has occurred. Because of the desired portability of the kit, the sought after closure must be light in weight and not be bulky.
The prior art includes at least one relatively small repair closure. See U.S. Pat. No. 4,820,007 which issued on Apr. 11, 1989 in the names of R. R. Ross and I. Vedejs. In it, a splice tray includes provisions on one side for holding optical fiber splices and metallic conductor splices on an opposite side. An electrical bonding and gripping assembly is adapted to be mounted on the splice tray. The closure also includes mating cover portions which are moved into engagement with each other to enclose the tray. Also, a waterblocking encapsulant may be introduced into the closure. See also application Ser. No. 07/736,850 (still pending) filed on Jul. 29, 1991 in the names of W. H. Bensel and G. S. Cobb.
Although the prior art of cable closures is highly developed, available closures have some shortcomings insofar as their temporary use in repair operations. For example, many commercially available closures include redundant sealing systems, provisions for ensuring water tightness, bonding and grounding, encapsulants and somewhat elaborate fastening arrangements for securing together portions of the closures. Also, the times required for the assembly of prior art closures are not insubstantial.
What is sought-after and seemingly what does not appear in the prior art is a closure which is relatively small and which is suitable for restoration installations for partial or total outages. The sought after closure must be relatively inexpensive, reusable, arranged for rapid assembly, not necessarily watertight and, of course, its use must not cause excessive bending to be introduced into the optical fiber.